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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 21 |
| 3 | 91 |
| 4 | 375 |
| 5 | 1487 |
| 6 | 5835 |
| 7 | 22775 |
| 8 | 88683 |
| 9 | 344975 |
| 10 | 1341395 |
| 11 | 5214791 |
| 12 | 20271307 |
| 13 | 78797247 |
| 14 | 306290211 |
| 15 | 1190562423 |
| 16 | 4627750267 |
| 17 | 17988173039 |
| 18 | 69920406547 |
| 19 | 271782019879 |
| 20 | 1056422029931 |
| 21 | 4106332901663 |
| 22 | 15961395217283 |
| 23 | 62042250575063 |
[4,21,91,375,1487,5835,22775,88683,344975,1341395, 5214791,20271307,78797247,306290211,1190562423, 4627750267,17988173039,69920406547,271782019879, 1056422029931,4106332901663,15961395217283, 62042250575063] |